2 files changed, 293 insertions, 0 deletions
diff --git a/game/terrain2.cpp b/game/terrain2.cpp
new file mode 100644
index 0000000..d1af221
--- /dev/null
+++ b/game/terrain2.cpp
@@ -0,0 +1,212 @@
+#include "terrain2.h"
+#include <fstream>
+#include <glm/gtx/intersect.hpp>
+#include <maths.h>
+
+TerrainMesh::TerrainMesh(const std::filesystem::path & input)
+{
+	size_t ncols = 0, nrows = 0, xllcorner = 0, yllcorner = 0, cellsize = 0;
+	std::map<std::string_view, size_t *> properties {
+			{"ncols", &ncols},
+			{"nrows", &nrows},
+			{"xllcorner", &xllcorner},
+			{"yllcorner", &yllcorner},
+			{"cellsize", &cellsize},
+	};
+	std::ifstream f {input};
+	while (!properties.empty()) {
+		std::string property;
+		f >> property;
+		f >> *properties.at(property);
+		properties.erase(property);
+	}
+	std::vector<VertexHandle> vertices;
+	vertices.reserve(ncols * nrows);
+	for (size_t row = 0; row < nrows; ++row) {
+		for (size_t col = 0; col < ncols; ++col) {
+			float height = 0;
+			f >> height;
+			vertices.push_back(add_vertex({xllcorner + (col * cellsize), yllcorner + (row * cellsize), height}));
+		}
+	}
+	if (!f.good()) {
+		throw std::runtime_error("Couldn't read terrain file");
+	}
+	for (size_t row = 1; row < nrows; ++row) {
+		for (size_t col = 1; col < ncols; ++col) {
+			add_face({
+					vertices[ncols * (row - 1) + (col - 1)],
+					vertices[ncols * (row - 0) + (col - 0)],
+					vertices[ncols * (row - 0) + (col - 1)],
+			});
+			add_face({
+					vertices[ncols * (row - 1) + (col - 1)],
+					vertices[ncols * (row - 1) + (col - 0)],
+					vertices[ncols * (row - 0) + (col - 0)],
+			});
+		}
+	}
+	update_face_normals();
+	update_vertex_normals();
+};
+
+OpenMesh::FaceHandle
+TerrainMesh::findPoint(glm::vec2 p) const
+{
+	return findPoint(p, *faces_begin());
+}
+
+TerrainMesh::PointFace::PointFace(const glm::vec2 p, const TerrainMesh * mesh) :
+	PointFace {p, mesh, *mesh->faces_begin()}
+{
+}
+
+TerrainMesh::PointFace::PointFace(const glm::vec2 p, const TerrainMesh * mesh, FaceHandle start) :
+	PointFace {p, mesh->findPoint(p, start)}
+{
+}
+
+TerrainMesh::FaceHandle
+TerrainMesh::PointFace::face(const TerrainMesh * mesh, FaceHandle start) const
+{
+	if (_face.is_valid()) {
+		assert(mesh->triangleContainsPoint(point, _face));
+		return _face;
+	}
+	else {
+		return (_face = mesh->findPoint(point, start));
+	}
+}
+
+TerrainMesh::FaceHandle
+TerrainMesh::PointFace::face(const TerrainMesh * mesh) const
+{
+	return face(mesh, *mesh->faces_begin());
+}
+
+namespace {
+	[[nodiscard]] constexpr inline bool
+	pointLeftOfLine(const glm::vec2 p, const glm::vec2 e1, const glm::vec2 e2)
+	{
+		return (e2.x - e1.x) * (p.y - e1.y) > (e2.y - e1.y) * (p.x - e1.x);
+	}
+
+	static_assert(pointLeftOfLine({1, 2}, {1, 1}, {2, 2}));
+	static_assert(pointLeftOfLine({2, 1}, {2, 2}, {1, 1}));
+	static_assert(pointLeftOfLine({2, 2}, {1, 2}, {2, 1}));
+	static_assert(pointLeftOfLine({1, 1}, {2, 1}, {1, 2}));
+
+	[[nodiscard]] constexpr inline bool
+	linesCross(const glm::vec2 a1, const glm::vec2 a2, const glm::vec2 b1, const glm::vec2 b2)
+	{
+		return pointLeftOfLine(a2, b1, b2) && pointLeftOfLine(a1, b2, b1) && pointLeftOfLine(b1, a1, a2)
+				&& pointLeftOfLine(b2, a2, a1);
+	}
+
+	static_assert(linesCross({1, 1}, {2, 2}, {1, 2}, {2, 1}));
+}
+
+OpenMesh::FaceHandle
+TerrainMesh::findPoint(glm::vec2 p, OpenMesh::FaceHandle f) const
+{
+	ConstFaceVertexIter vertices;
+	while (f.is_valid() && !triangleContainsPoint(p, vertices = cfv_iter(f))) {
+		for (auto next = cfh_iter(f); next.is_valid(); ++next) {
+			f = opposite_face_handle(*next);
+			if (f.is_valid()) {
+				const auto e1 = point(to_vertex_handle(*next));
+				const auto e2 = point(to_vertex_handle(opposite_halfedge_handle(*next)));
+				if (pointLeftOfLine(p, e1, e2)) {
+					break;
+				}
+			}
+			f.reset();
+		}
+	}
+	return f;
+}
+
+glm::vec3
+TerrainMesh::positionAt(const PointFace & p) const
+{
+	glm::vec3 out {};
+	Triangle<3> t {this, fv_range(p.face(this))};
+	glm::intersectLineTriangle(p.point ^ 0.F, up, t[0], t[1], t[2], out);
+	return p.point ^ out[0];
+}
+
+[[nodiscard]] std::optional<glm::vec3>
+TerrainMesh::intersectRay(const Ray & ray) const
+{
+	return intersectRay(ray, findPoint(ray.start));
+}
+
+[[nodiscard]] std::optional<glm::vec3>
+TerrainMesh::intersectRay(const Ray & ray, FaceHandle face) const
+{
+	std::optional<glm::vec3> out;
+	walkUntil(PointFace {ray.start, face}, ray.start + (ray.direction * 10000.F), [&out, &ray, this](FaceHandle face) {
+		glm::vec2 bari {};
+		float dist {};
+		Triangle<3> t {this, fv_range(face)};
+		if (glm::intersectRayTriangle(ray.start, ray.direction, t[0], t[1], t[2], bari, dist)) {
+			out = t * bari;
+			return true;
+		}
+		return false;
+	});
+	return out;
+}
+
+void
+TerrainMesh::walk(const PointFace & from, const glm::vec2 to, const std::function<void(FaceHandle)> & op) const
+{
+	walkUntil(from, to, [&op](const auto & fh) {
+		op(fh);
+		return false;
+	});
+}
+
+void
+TerrainMesh::walkUntil(const PointFace & from, const glm::vec2 to, const std::function<bool(FaceHandle)> & op) const
+{
+	assert(from.face(this).is_valid()); // TODO replace with a boundary search
+	auto f = from.face(this);
+	FaceHandle previousFace;
+	while (f.is_valid() && !op(f)) {
+		for (auto next = cfh_iter(f); next.is_valid(); ++next) {
+			f = opposite_face_handle(*next);
+			if (f.is_valid() && f != previousFace) {
+				const auto e1 = point(to_vertex_handle(*next));
+				const auto e2 = point(to_vertex_handle(opposite_halfedge_handle(*next)));
+				if (linesCross(from.point, to, e1, e2)) {
+					previousFace = f;
+					break;
+				}
+			}
+			f.reset();
+		}
+	}
+}
+
+bool
+TerrainMesh::triangleContainsPoint(const glm::vec2 p, const glm::vec2 a, const glm::vec2 b, const glm::vec2 c)
+{
+	const auto det = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
+
+	return det * ((b.x - a.x) * (p.y - a.y) - (b.y - a.y) * (p.x - a.x)) >= 0
+			&& det * ((c.x - b.x) * (p.y - b.y) - (c.y - b.y) * (p.x - b.x)) >= 0
+			&& det * ((a.x - c.x) * (p.y - c.y) - (a.y - c.y) * (p.x - c.x)) >= 0;
+}
+
+bool
+TerrainMesh::triangleContainsPoint(const glm::vec2 p, FaceHandle face) const
+{
+	return triangleContainsPoint(p, cfv_iter(face));
+}
+
+bool
+TerrainMesh::triangleContainsPoint(const glm::vec2 p, ConstFaceVertexIter vertices) const
+{
+	return triangleContainsPoint(p, point(*vertices++), point(*vertices++), point(*vertices++));
+}
diff --git a/game/terrain2.h b/game/terrain2.h
new file mode 100644
index 0000000..5539a50
--- /dev/null
+++ b/game/terrain2.h
@@ -0,0 +1,81 @@
+#pragma once
+
+#include "collections.h" // IWYU pragma: keep IterableCollection
+#include "ray.h"
+#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
+#include <filesystem>
+#include <glm/vec2.hpp>
+#include <optional>
+#include <thirdparty/openmesh/glmcompat.h>
+
+struct TerrainTraits : public OpenMesh::DefaultTraits {
+	FaceAttributes(OpenMesh::Attributes::Normal | OpenMesh::Attributes::Status);
+	EdgeAttributes(OpenMesh::Attributes::Status);
+	VertexAttributes(OpenMesh::Attributes::Normal | OpenMesh::Attributes::Status);
+	HalfedgeAttributes(OpenMesh::Attributes::Normal | OpenMesh::Attributes::Status);
+	using Point = glm::vec3;
+	using Normal = glm::vec3;
+};
+
+class TerrainMesh : public OpenMesh::TriMesh_ArrayKernelT<TerrainTraits> {
+public:
+	explicit TerrainMesh(const std::filesystem::path &);
+
+	struct PointFace {
+		// NOLINTNEXTLINE(hicpp-explicit-conversions)
+		PointFace(const glm::vec2 p) : point {p} { }
+
+		PointFace(const glm::vec2 p, FaceHandle face) : point {p}, _face {face} { }
+
+		PointFace(const glm::vec2 p, const TerrainMesh *);
+		PointFace(const glm::vec2 p, const TerrainMesh *, FaceHandle start);
+
+		const glm::vec2 point;
+		[[nodiscard]] FaceHandle face(const TerrainMesh *) const;
+		[[nodiscard]] FaceHandle face(const TerrainMesh *, FaceHandle start) const;
+
+		[[nodiscard]] bool
+		isLocated() const
+		{
+			return _face.is_valid();
+		}
+
+	private:
+		mutable FaceHandle _face {};
+	};
+
+	template<glm::length_t Dim> struct Triangle : public glm::vec<3, glm::vec<Dim, glm::vec2::value_type>> {
+		using base = glm::vec<3, glm::vec<Dim, glm::vec2::value_type>>;
+		using base::base;
+
+		template<IterableCollection Range> Triangle(const TerrainMesh * m, Range range)
+		{
+			assert(std::distance(range.begin(), range.end()) == 3);
+			std::transform(range.begin(), range.end(), &base::operator[](0), [m](auto vh) {
+				return m->point(vh);
+			});
+		}
+
+		glm::vec<Dim, glm::vec2::value_type>
+		operator*(glm::vec2 bari) const
+		{
+			const auto & t {*this};
+			return t[0] + ((t[1] - t[0]) * bari.x) + ((t[2] - t[1]) * bari.y);
+		}
+	};
+
+	[[nodiscard]] FaceHandle findPoint(glm::vec2) const;
+	[[nodiscard]] FaceHandle findPoint(glm::vec2, FaceHandle start) const;
+
+	[[nodiscard]] glm::vec3 positionAt(const PointFace &) const;
+	[[nodiscard]] std::optional<glm::vec3> intersectRay(const Ray &) const;
+	[[nodiscard]] std::optional<glm::vec3> intersectRay(const Ray &, FaceHandle start) const;
+
+	void walk(const PointFace & from, const glm::vec2 to, const std::function<void(FaceHandle)> & op) const;
+	void walkUntil(const PointFace & from, const glm::vec2 to, const std::function<bool(FaceHandle)> & op) const;
+
+protected:
+	[[nodiscard]] static bool triangleContainsPoint(const glm::vec2, const glm::vec2, const glm::vec2, const glm::vec2);
+	[[nodiscard]] bool triangleContainsPoint(const glm::vec2, FaceHandle) const;
+	[[nodiscard]] bool triangleContainsPoint(const glm::vec2, ConstFaceVertexIter) const;
+};